% 结合DFT矩阵和IDFT矩阵实现线性卷积和
function y = fd_conv(x1, x2)
    N1 = length(x1);
    N2 = length(x2);
    
    N = N1 + N2 - 1;
    
    X1 = fft(x1, N);
    X2 = fft(x2, N);
    
    Y = X1 .* X2;
    
    y = ifft(Y);
end